Despite all the advances in battery technologies, pumped hydro storage--essentially pumping water uphill and releasing it through a generator later--remains one of the cheapest ways to store bulk electricity on the grid.
California utility Pacific Gas & Electric on Friday filed a request with state regulators to fund a feasibility study for adding a pumped hydro facility which could store as much energy as a power plant can supply.
PG&E has identified the Mokelumne River watershed in Amador County, Calif., as a location. The utility wants to study placing a pumped hydro facility sized between 400 megawatts and 1,200 megawatts. One thousand megawatts is the size of one large or two medium-size power plants.
Typically, pumped hydro facilities have two reservoirs with water pumped uphill during off-peak times and released during peak times. PG&E said that adding more storage will allow it to better accommodate wind and solar power, which are variable sources of power.
There are at least three other pumped hydro storage projects under consideration in California, according to the PG&E company blog Next 100.
In the past two years, there's been a resurgence in interest in energy storage on the grid, where a number of technologies are vying for different uses.
Pumped hydro and storing compressed air underground are well-suited for storing large amounts of energy which can be supplied for many hours. The obvious limitation to these geological-based approaches is the lack of available locations and the potential local environmental impact.
Utilities are experimenting with different batteries, too, which can provide 1 or 2 megawatts for up to a few hours, although these systems are considered very costly. Another technology is flywheels, which are used to maintain a steady frequency on the grid by storing and providing small amounts of energy very quickly.
Despite the cost, many people expect grid storage to grow and provide a number of applications, including backing up intermittent wind and solar or providing energy during peak times.